In U.S. Pat. Nos. 3,479,395, 3,637,515, 3,668,239, 3,689,535, 3,715,388, 3,715,389, 3,743,672, 3,789,065, 3,907,874, 3,985,795, 4,045,477 and 4,073,876 there is disclosed processes for the preparation of vicinal glycol esters by the liquid phase oxidation of an olefin, such as ethylene or propylene in a carboxylic acid medium, such as acetic acid using a tellurium catalyst and a source of halide ions.
The present invention is directed to an effective method of recovering the tellurium from vicinal glycol ester solutions produced, for example, by such above described processes and containing tellurium in the form of soluble inorganic tellurium compounds and organotellurium compounds. Because of the high reactivity of tellurium, in combination with a halide source when used as a catalyst as in the above reaction its combination with organic compounds such as the carboxylic acids and olefins employed very frequently results in the formation of organo-tellurium compounds, such as tetra and divalent alkyl tellurium halides, tellurium carboxylate compounds and the compounds described for example in an article by Jan Bergman, Kemisk Tedskrift, Vol. 88 (11) pp. 62-3, 1976, Sweden, entitled New Production Process for Ethylene Glycol as well as other soluble tellurium compounds which remain in solution with the glycol ester reaction product. In such reaction, a portion of the tellurium catalyst such as tellurium dioxide, etc. is itself or in combination with the halide source, converted to one or more organotellurium compounds. The type and number of organotellurium compounds which may be formed is a function of the reaction conditions to produce the vicinal glycol ester such as time, temperature, carboxylic acid and any solvent which might be employed. In addition, at least some of the inorganic tellurium compounds used as catalysts or formed in the reaction, such as tellurium tetrabromide, may also remain in solution with the glycol ester product.
Because of the cost and toxicity of tellurium, it is essential that as much of the tellurium be recovered from the glycol ester reaction product as is possible and from the inorganic or organotellurium compounds in a form suitable for reuse as a catalyst.
There is no known prior art which describes the removal and recovery of soluble inorganic or organotellurium compounds from a vicinal glycol ester product by adsorption on granular activated carbon and prepared by the tellurium catalyzed acetoxylation of olefins.